What the Alliance report fails to tell you are the margins of error, which really give you an idea how inaccurate these numbers are.

That 2009 number is 1,217 plus or minus 803. Yep, the Census says the actual 2009 number could be as low as 414, likely within the 1990 number’s margin of error.

Another thing to consider: The 2009 numbers are based on a Detroit population of over 900,000, which is off by couple hundred thousand people.

And while everyone acknowledges Detroit’s notable increase in cycling activity last year, the 2010 Census numbers show bicycle commuting dropped nearly in half to 651 plus or minus 424.

If this hasn’t convinced you these numbers are quite worthless, there’s more.

The Census numbers only includes those who are working and 16 years or older. The Census doesn’t count most people who combine modes (e.g. use the bus bike racks) or who bike only a couple times a week.

The Alliance for Biking and Walking were made aware of these Census discrepancies for Detroit, but for the most part they did not address them. That’s why Detroit chose not to participate in the most recent report.

Other cities

Other cities are making big strides in understanding bicycling trends and counts. They’re doing travel surveys and bicycle counts — both automatically and manually — at key bridges and intersections.

Detroit’s done some bicycle counts around Woodward, in Southwest Detroit, and on the RiverWalk, but not enough to draw any major conclusions. It would great if some future bike lane projects (looking at you, E. Jefferson!) could get some automated counters.

Mayor Bing posted on Facebook, “I am confident our count will be revised. We must confront the reality that Detroit is losing population and commit to operating differently.”

How does this affect bicycling in Detroit?

If there is a positive, this population count reconfirms what we’ve been saying about the city’s urban biking. Detroit’s roads are some of the most bike friendly in America because more motorists are leaving them. The Detroit Census count has not been this low since 1910. And though we have greater car ownership in 2010, we also have many more road miles, not to mention expressways.

That said, there are many downsides to a dropping population.

For one, Detroit stands to lose road funding, which means less opportunity for building Complete Streets.

State road funding is divided up in an overly complex formula based on decades of legislative tweaks. Still, each city and village receives a portion of road funding based in part on their population relative to the others. When a city’s population drops more than the other citys and villages, they get less road funding. We’re not sure how much Detroit will lose, but we know it won’t be welcomed.